This invention relates generally to the field of telephony, and more particularly to improved telephone protector module construction for use with individual subscriber circuits used to protect central office equipment from damage caused by the transmission of excessive current surges. Devices of this general type are known in the art, and the invention lies in specific constructional details which provide an additional function of the module with the firing of a heat-sensitive device incorporated therein.
Protective modules of known type are placed on telephone office main frames, and when connected in series with a subscriber line serve to ground the line upon the occurrence of excessive current surges, such as results from lightning strikes, contact with fallen power cables and the like. While some modules, particularly those used in rural areas often employ carbon electrodes or a gas tube in the absence of other protective components, more sophisticated modules employ some kind of heat sensor or heat coil which will melt a solder pellet or solder seal upon the occurrence of continuous excessive current. When the solder melts, a resiliently urged member moves to establish a permanent short to ground, thereby protecting the office equipment.
In the case of most conventional equipment, such protection has proven adequate. However, in recent years, there has been a substantial amount of privately owned equipment installed in shaftways in tall buildings, in which the danger of fire is ever present. That portion of a protective circuit disposed within the building can be accidentally damaged by repair or alteration of the building interior, and other causes beyond the control of the telephone company. It is desirable that such part of the circuit be placed in non-conductive condition upon the occurance of an excess current surge rather than merely grounded.